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I had to catch up on some yard work today. I also had several books to try and finish. I had started them a while ago and kept getting side tracked. I was starting to feel guilty about not posting anthing today – then I noticed a lot of blogs have posted little to nothing. Now I don’t feel so bad.

One of the books I am trying to get through is “New Directions in Ecological Physiology” by Feder et al. One of the chapters (chapter 8: The Importance of Genetics to Physiological Ecology, by Richard Koehn) mentioned something that got me to thinking. But first, a little background for the genetically impaired- um, that came out wrong, I should say for those who are not very familiar with the science of genetics. For those of you who are familiar with genetics I apologize in advance for the intro material.

Genes can come in more than one form (alleles). For example, a gene can have two alleles- call them A and a. From these two alleles you can derive three possible genotypes AA, Aa and aa. Genotypes AA and aa are called homozygous and genotype Aa is called heterozygous. In a system lacking selection the frequency of the heterozygous genotype is contingent on the frequencies of A and a. Using Hardy-Weinberg one can calculate the frequency of Aa fairly simply.When selection is present things become a little more difficult. Take sickle cell anemia. Sickle cell anemia is a recessive disease which causes red blood ceels to collapse into a sickle shaped cell. Terminology for the gene varies and I will use the Hb terminology. Basically, Hb A HbA is normal Hb S Hb S is the homozygote recessive – which is fatal – and Hb A Hb S are heterzygotes. Because having Hb A Hb S confers a certian amount of immunity to malaria this genotype enjoys a slight selective advantage over Hb A HbA. Even though there is selection for the heterozygote, we can still calculate the frequency. We just have to know the amount of selection and include a term for it in our formula for estimating gene frequencies.Another interesting question is how many genes in a given genome are heterozygotic. I don’t have figures at hand, but the answer is quite a few. So the next question is- leaving aside when heterozygotes have a selective advantage – are there any other advantages in having a large number of heterozygous genes.Apparently, the answer is yes – at least in some species. Which brings us back to the above mentioned chapter in “New Directions in Ecological Physiology”. Koehn reviews several studies which demonstrate that heterozygosity (and here I am refering to heterozygosity at the enzyme level) increase metabolic efficiency, resulting in energy savings. These energy savings can be channeled into any number of different areas – growth or increased feeding rates to name a few. Or (this is afarensis extrapolating) perhaps into new adaptations that allow for expanded niches or moves into new niches? Or to provide the energy for co-opting other traits and making something new out of them?

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"You may not be willing to admit that you resemble an ape; if your thousandth ancestor is more like an ape than you are, you may, if you wish, call it a coincidence. But if that thousandth ancestor's forebears become progressively more simian as you trace back the geneological lines, you will have to admit that somewhere in your family tree there squats an ape." Earnest Hooten

Charles Darwin

"But I had gradually come, by this time, to see that the Old Testament from its manifestly false history of the world, with the Tower of Babel, the rainbow at sign, etc., etc., and from its attributing to God the feelings of a revengeful tyrant, was no more to be trusted than the sacred books of the Hindoos, or the beliefs of any barbarian." Charles Darwin: The Autobiography